1. Field of the Invention
The present invention relates to a reinforced hose and, more particularly, to a hose reinforced by strands and used in a hydraulic circuit, such as a water hose, an oil hose, a brake hose, or a fuel hose in vehicles.
2. Description of Related Art
Technical arts for a reinforced hose are already disclosed in U.S. Pat No. 4,111,237 and U.S. Pat. No. 4,998,565. In these patents, the reinforced hose, as shown in FIGS. 3 and 4, has an inner tube 91 made of rubber, an inner reinforcing layer 92 formed on the inner tube 91 by strands 921, an intermediate layer 93 made of rubber formed on the inner reinforcing layer 92, an outer reinforcing layer 94 formed on the intermediate layer 93 by strands 941, and a covering layer 95 made of rubber formed on the outer reinforcing layer 94. This type of reinforced hose is usually used for transferring high pressured fluid and/or transmitting high pressure in the hydraulic circuit, for example, such as in an oil hose.
Recently, in order to increase the stretching strength to reduce expansion and to increase the heat durability of hoses, the strands of both the inner and outer reinforcing layers have been made of aromatic polyamide type yarn. Therefore, these reinforced hoses have good performance for a bursting pressure over 2,300 kg/cm.sup.2. However, as the aromatic polyamide type yarn is hard to shrink, but the inner tube 91 and the intermediate layer 93, because they are made of rubber, are shrunk by the heat of a curing process. A small gap is formed between the inner tube 91 and the inner reinforcing layer 92, and between the intermediate layer 93 and the outer reinforcing layer 94. As a result, the inner tube 91 will expand due to the pressure of inside fluid. The pressure in conventional reinforced hoses having 3.1 mm in diameter vs. expansion of the hose is shown in FIG. 2. In accordance with this graph, these types of conventional reinforced hoses have a large volume of expansion under any given pressure of up to 100 kg/cm.sup.2 which is usually used. Therefore, conventional reinforced hoses sometimes cause an insufficient response time in a hydraulic circuit since expansion slows the fluid effect.